Air Interface The UTRAN air interface uses QPSK or 16QAM. The modulation chip rate is 3.84 Mcps. There are two dedicated physical channels; DPCCH (for control information) and the DPDCH (for user data). UMTS Channel structure: Logical channels define what type of data is transferred. Transport channels define how and with which type of characteristics the data is transferred by the physical layer. Physical channels data define the exact physical characteristics of the radio channel.